JPH0797228B2 - Electrophotographic device and its medium - Google Patents

Abstract

An improved enhancement layer (18) operatively disposed between the top protective layer (19) and the photoconductive layer (16) of an electrophotographic device (10). The enhancement layer (18) is specifically tailored from a semicondcutor alloy material designed to substantially prevent charge carriers from being caught in deep midgap traps as said carriers move toward the surface of the electrophotogrpahic device (10) from the photoconductive layer (16) thereof. A method of substantially improving charge fatigue characteristics through the use of such an improved enhancement layer (18) is also disclosed.

Description

FIELD OF THE INVENTION The present invention relates generally to electrophotographic devices and media. More specifically, intentionally or heavily doped to substantially reduce the trapping of charge carriers in the deep intermediate gap state (deep state in the center of the gap).
d) A medium for an electrophotographic apparatus having an improved enhancement layer configured to substantially eliminate charge fatigue of an electrophotographic photoreceptor by forming the enhancement layer from a semiconductor alloy material, and such a medium are provided. Related to electrophotographic apparatus.

BACKGROUND OF THE INVENTION The present invention relates to electrophotographic device media having improved enhancement layers for use in electrophotographic imaging or imaging processes and electrophotographic devices equipped with such media. The improved enhancement layer of the present invention is formed from a semiconductor alloy, which is characterized by a reduced number of defects in the center of the deep gap that traps charge carriers.
By reducing the number of deep traps, the rate of charge carrier emission from the traps is increased, effectively eliminating the charge fatigue problem common in conventional electrophotographic media.

Electrophotographic technology, commonly referred to as xerography, is an imaging method that operates by the accumulation and release of electrostatic charges by a photoconductive material. Photoconductive materials are lighting,
That is, it becomes conductive in response to absorption of incident light and becomes a pair of electrons and holes (“charge carrier”) inside the photoconductive material.
(Also called) is a material that produces. It is the charge carriers that pass an electric current through the material to discharge the electrostatic charge, which in standard electrophotography accumulates charge on the outer surface of the electrophotographic medium.

A standard photoreceptor generally comprises a cylindrical conductive substrate member formed of a metal such as aluminum. In addition to this, the substrate may be in the form of a flat sheet, a curved sheet, a metal-treated flexible belt, or the like. The photoreceptor also includes a photoconductive layer. As described above, the photoconductive layer is formed of a photoconductive material having a relatively low conductivity in the dark and a high conductivity under illumination. Disposed between the photoconductive layer and the substrate member is a barrier layer, which layer is formed from a layer of a naturally occurring oxide or semiconductor alloy deposited on the substrate member. As described in more detail below, the barrier layer serves to prevent unwanted charge carriers from flowing into the photoconductive layer from the substrate member. If the charge carriers enter the photoconductive layer, they may neutralize the charge accumulated on the surface of the photoreceptor.

Standard photoreceptors also generally include a surface protective layer, which is disposed over the photoconductive layer to stabilize the acceptance of electrostatic charge against changes due to adsorbed species and to protect the light. Improves the durability of the receptor. Finally, the photoreceptor may operatively include an enhancement layer between the photoconductive layer and the surface protective layer. The enhancement layer is configured to substantially prevent trapping of charge carriers in the deep traps and, consequently, photoreceptor charge fatigue.

In order to obtain high resolution copies, it is desirable for the electrophotographic photoreceptor to accept and retain a high electrostatic charge in the dark. Also, it is necessary to take measures to prevent the charge carriers forming the charge from flowing from the respective parts of the photoreceptor to the grounded substrate or from the substrate to the charged parts of the photoreceptor under illumination. And it is necessary to hold substantially all of the initial charge for a suitable period of time without substantially attenuating it in the non-illuminated part. Image-wise discharge of the photoreceptor occurs by the photoconductive process described above. However, unwanted discharge may occur via charge injection at the top or bottom and / or charge carrier generation by internal heat in the photoconductive material.

The main source of charge injection is at the interface between the metal substrate and the semiconductor alloy. The metal substrate becomes essentially a sea of electrons which can be used to neutralize, for example, the positive electrostatic charge on the photoreceptor surface after electron injection.

All of the actual electrophotographic media have a bottom barrier layer between the substrate and the photoconductive member because these electrons would immediately flow into the photoconductive layer if there were no obstacles.

One of the particularly important operational problems of conventional electrophotographic media is the inherent properties of semiconductor alloys forming layers of conventional structure, such as charge carriers between the photoconductive layer and the surface protective layer. When it reaches the interface, there is a problem due to the inherent property that charge carriers are confined in the deep energy gap of the alloy material.

Such a condition is known as charge fatigue and occurs when charge carriers cannot escape from the trap quickly, resulting in the disruption of the shielding function of the surface protective layer. When the surface protection layer is destroyed, the flow of charge carriers is free to move through it in an attempt to neutralize the electrostatic charge on the surface of the electrophotographic medium. Along with this problem, the solution of the present inventor will be described in detail in the next section.

During normal electrophotographic process operation, a positive corona charge is present on the outer surface of the electrophotographic medium (exposed surface of the surface protective layer). In response to the application of this positive charge to the upper surface of the electrophotographic medium, the electrophotographic medium photoconductive layer sweeps all free electrons from the inside toward the upper surface of the medium as the first reaction, and the positive charge on the upper surface Try to neutralize. However, when such an electron moves from the inside of the photoconductive layer to the outer surface of the surface protective layer (where positive charge carriers are accumulated on it), the electron is deep as in an intermediate gap defect state. Encounter a trap. The location of such a trap exists over the entire inside of the photoconductive layer, and is particularly important when the trap is located near the interface between the photoconductive layer and the surface protective layer.
It has a shielding function when there is a strong electric field across the surface protection layer (prevents positive charge carriers electrostatically placed around the surface protection layer from entering the surface protection layer). This is because the effectiveness of is lost ("destroys"). Confinement of a constant density of negative charge carriers near the aforementioned interface between the surface protective layer and the photoconductive layer creates an electric field across the surface protective layer that is strong enough to cause breakdown. Is clear. In contrast, even if the same number of negative charge carriers are confined inside the photoconductive layer, this does not occur.

Further, the trapping site in the deep energy gap of the semiconductor alloy has a slower rate of releasing trapped charge carriers than the trapping site existing close to either the conduction band or the valence band. This is because, for example, when re-exciting trapped electrons from a deep location near the middle of the energy gap toward the conduction band, it requires more thermal energy than re-exciting electrons from a shallow location closer to the conduction band. Is. Since the emission rate from the deep trap is slow, the equilibrium trap occupancy rate and thus the electric field distribution are high.

In the manufacture of a typical electrophotographic photoreceptor that operates by applying a positive corona charge to its outer surface, its photoconductive layer is made of a "pi (π) type" silicon-fluorine-hydrogen-boron alloy. It is necessary to pay attention to the formation. As used herein, the term "pi-type" means that the Fermi level is almost "intermediate gap" from the undoped location near the conduction band.
Refers to a semiconductor alloy that has been displaced to the location. Further, the terms "intermediate gap" to "center of the gap" used herein refer to a point in the energy gap of a semiconductor alloy, which is located halfway between the valence band and the conduction band (1.8e).
For V amorphous silicon / fluorine / hydrogen / boron alloys, this point is about 0.9 eV from each band). It is necessary for the photoconductive layer of the photoreceptor to be pi-typed by standard "intrinsic" amorphous silicon deposited by glow discharge decomposition.
The hydrogen-fluorine alloy becomes slightly "nu (μ) -type" (the Fermi level of the material is slightly closer to the conduction band than the valence band), and under illumination in the electrophotographic process by the positive corona charge. This is because the movement of the charge carriers through the photoconductive layer must be maximized while at the same time heat generation of the charge carriers must be minimized.

When the Fermi level is placed in the intermediate gap (such as after adding a p-type dopant to a silicon-fluorine-hydrogen alloy material), electrons moving through the p-type material encounter deep traps that cannot easily escape. It requires attention to do. This is because the deepest electron trapping site in the layer of semiconductor alloy material is at or near the Fermi level, and for such a pi-type material this energy coincides with the intermediate gap. The thermal energy required to release an electron from a deep trap depends on the depth of the trap. More specifically, the average time taken for heat to be released from a trap in a trapped electron is the number of electrons trying to escape ν ₀ in 1 second, and ΔE is the number of electrons from the Fermi level to the conduction band edge. Energy required to move, kT
Where is the product of the absolute temperature and the Boltzmann constant, it is given by the equation t = [ν ₀ EXP (−ΔE / kT)]. It can be estimated that the value of ν ₀ is almost 10 ¹² / sec in most solids. Therefore, when the Fermi level position is 0.9 eV (intermediate gap), the emission time at room temperature is 4 × 10 ³ . The fact that the escape time is long in this way is almost 1.
It means that it will take 2 hours. Of course, such slow electron emission rates cannot be tolerated in electrophotographic photoreceptors. If the electrons are once trapped for such a long time, the concentration of the electrons trapped at the interface between the photoconductive layer and the surface protective layer will be high, and the charge in this space and the surface of the surface protective layer will increase. With a positive charge that accumulates on the surface protection layer will create a very high electric field distortion. Then, this electric field causes "breakage" of the surface protective layer. As used herein, the term "breakdown" refers to the inability of the surface protection layer to block the flow of charge carriers therethrough.

The inventor has discovered that this reduction in breakdown can be eliminated by reducing the number of defect states that cause deep charge carrier traps. US Patent Application No. 580,081 of the present inventor dated February 14, 1984 (corresponding patent application Sho 60-28161).
No. 4) as disclosed in "Method for improved formation of photoconductive member and improved photoconductive member formed thereby", operatively disposing an "enhancement layer" between the surface protective layer and the photoconductive layer. The performance of the electrophotographic apparatus incorporating the layer can be improved. Although the physical behavior of the enhancement layer was not clear at the time of filing the 580,081 application, the applicant recently confirmed that the enhancement layer (formed by the method disclosed in the above patent application) ) Acts to reduce the overall defect density in the material that forms the enhancement layer, thereby reducing the time it takes for charge carriers to escape from being trapped in the deep traps encountered at the photoconductive layer interface. do. However, the enhancement layer described in the above-mentioned pendant application is not a microwave glow discharge (because microwave deposition tends to increase the defect state) but an intrinsic semiconductor alloy material is deposited by radio frequency (high frequency) glow discharge, The method has been to reduce the overall defect density. Therefore, the enhancement layer of the above application relies on reducing the overall defect density present in undoped semiconductor alloy materials to reduce the number of deep traps that are likely to trap charge carriers and reduce charge fatigue. No further discussion of optimizing the chemical composition of the enhancement layer to prevent charge carriers from being trapped in deep traps in the intermediate gap was made in the application and no attempt was made to do so. Not not.

The main advantage obtained by the present disclosure is to optimize the enhancement layer to prevent charge carrier fatigue, and to improve the operation cycle and repetition time of an electrophotographic apparatus incorporating this optimized enhancement layer. There is something that can be improved. Further, by using the present disclosure, charge carriers can be substantially prevented from falling into deep traps in the intermediate gap. Although only relatively thick defect states can remain and trap the charge carriers therein, the rate of charge carrier release from the shallow trap is measurable in seconds, not days. Therefore, in its broadest form, the present application relates to placing the Fermi level of the semiconductor alloy material forming the enhancement layer at a position above the intermediate gap.

As a result, since the deep intermediate gap state is occupied by electrons, the effect as an electron trap is lost. Thus, the electrons working through the enhancement layer do not have to pass through the region with the effective deep intermediate gap trap. In other words, in a 1.8 eV silicon-hydrogen-fluorine-phosphine alloy, its Fermi level is 0.75 to 0 from the conduction band.
In the most desirable range of 65 eV, the electron escape time is about 1 second or less. Due to the short release time, the charge trapped in this region is virtually eliminated and the high electric field distortion is eliminated. Similarly, when using a negative charge, the Fermi level of the enhancement layer is 0.75 ~ from the valence band.
Placement at 0.65 eV allows the trapped carriers to be released as quickly as well.

Note that the inventors of the present invention do not claim to have invented the concept of fixing the Fermina level of the amorphous semiconductor alloy material forming one of the working layers of the electrophotographic photoreceptor. I want to be done. The inventor claims that by fixing the Fermi level of the semiconductor alloy material that forms the enhancement layer at a point of approximately 0.8 to 0.5 eV from either the conduction band or the valence band, the charge carriers are deep The point is that it was confirmed for the first time that it was possible to substantially prevent the trapping in the intermediate gap trap.

The discovery of the inventor was found in "Journal
Of Applied Physics "(Journal of Appli
ed Physics) Mort et al. (Page 3197)
This is in clear contrast to the technique described in the paper of l), "Field Effect Phenomena in Hydrogenated Amorphous Silicon Photoreceptors". In this paper, Mote et al. Describe a method of eliminating the electric field effect in the photoreceptor, which is accomplished by appropriately doping the interface between a-Si: H and the insulator. Mort et al. Propose that the adverse effect of the Fermi level under the influence of the electric field generated by corona charging of the photoreceptor for electrophotography is countered by doping. More specifically, Mohto et al. Eliminate the electric field effect by arranging a boron-doped trap layer between the upper surface of the photoconductive layer and the insulating layer (surface protective layer) to eliminate the "electric field blurring". He proposed to eliminate the effect of "(commonly referred to as" image-flow "). "Flow of images" in this way
It can be said that it succeeded in countering the problem.

However, Mote et al. Are not paying attention to the problem of "charge fatigue" that exists at the same time. Moreover, the Fermi level of the semiconductor alloy material shifts toward the valence band by adding the boron dopant. Such a transition of the Fermi level of the semiconductor alloy material results in the electrons trying to move toward the conduction band passing through a deep intermediate gap state, which is the cause of the charge fatigue problem. That is the problem that the present application seeks to avoid. Mort et al., Suspect that using phosphorous doping to move the Fermi level of the enhancement layer towards the conduction band enhances the conductivity of the semiconductor alloy, thereby producing lateral electron flow that they seek to prevent. It is noted that the use of phosphorus doping is specifically prohibited.

On the contrary, the inventor first strongly doped the semiconductor alloy material of the enhancement layer arranged between the photoconductive layer and the surface protection layer with phosphorus and moved the Fermi level of the material toward the conduction band. . This shift of the Fermi level of the semiconductor alloy material eliminates the need for the electrons to be trapped in the deep intermediate gap state in which the energy gap exists. By keeping the electrons outside the deep intermediate gap state in this way, the problem of charge fatigue can be substantially eliminated. Next, both the boron dopant and the phosphorus dopant are introduced to add defect states on both sides of the Fermi level, thereby fixing the Fermi level at a predetermined position in the energy gap. Since the defect state added at this time is shallow, not only the problem of charge fatigue can be solved, but also the number is sufficient, so that side electron flow is blocked, field effect is quenched, and at the same time, the problem of image flow is also solved. .

As is clear from the above discussion, Mote et al. Propose a solution to the problem of image flow in electrophotographic media, but do not consider the problem of charge fatigue caused by the solution to image flow. . On the other hand, the present invention can solve both problems by first appropriately moving and then fixing the Fermi level of the semiconductor alloy material of the newly added enhancement layer.

In light of the definitions used in the various chemical and patent literature for the terms "amorphous" and "microcrystalline", it may be helpful to clarify the definitions of these terms as used herein. As used herein, the term "amorphous" refers to an alloy or material that exhibits short-range or medium-range order, for example, or that does not have long-range order even if it contains crystalline inclusions. Is defined as including. As used herein, the term "microcrystalline" is a material that belongs to a part of the above-mentioned amorphous materials, and the volume ratio of crystalline inclusions depends on certain key parameters such as conductivity, bandgap, and absorption constant. Is defined as being greater than a threshold at which a dynamic change begins. It should be noted that, according to the above definitions, the materials used in the practice of the present invention fall within the generic term "amorphous" defined above.

These and other objects and advantages of the present invention will be apparent from the following detailed description of the invention, the brief description of the drawings and the appended claims.

SUMMARY OF THE INVENTION Disclosed herein is an electrophotographic medium over a conductive substrate, a bottom barrier layer overlying the substrate, and a bottom barrier layer configured to block the free flow of charge carriers from the substrate. A photoconductive layer that is stacked and configured to emit an electrostatic charge and a photoconductive layer that is stacked on the photoconductive layer and is configured to substantially reduce the number of charge carriers trapped in a deep intermediate gap trap. , A semiconductor layer formed intentionally or strongly doped with a semiconductor alloy material, i.e., an enhancement layer and a photoconductive layer overlying the enhancement layer to protect the photoconductive layer from environmental conditions and to charge under illumination. And a surface protection layer configured to aid in carrier transport. The bottom barrier layer is a doped microcrystalline semiconductor selected from the group consisting essentially of chalcogens, amorphous silicon alloys, amorphous germanium alloys, amorphous silicon-germanium alloys, photoconductive organic polymers and combinations thereof. It is preferably formed of an alloy material.
The enhancement layer is preferably formed of a material selected from the group consisting essentially of amorphous silicon alloys, amorphous germanium alloys, and amorphous silicon-germanium alloys. Further, it is more preferable that the enhancement layer is formed of an amorphous silicon alloy and the Fermi level thereof is moved within the range of 0.5 to 0.8 eV of the conduction band or the valence band. In a more preferred embodiment, the Fermi level of the enhancement layer is moved within the range of 0.65 to 0.75 eV from the conduction or valence band. Thus, the enhancement layer is formed from a material specifically configured to release heat of charge carriers from the traps at the interface between the enhancement layer and the surface protective layer for 1 second or less. The thickness of the enhancement layer is approximately 2,500-10,000 angstroms,
It is preferably 5,000 Å. The Fermi level of the enhancement layer may be fixed at a certain position from the conduction band. The Fermi level is fixed by adding both phosphorus and boron to the base of the semiconductor alloy and adding a shallow state to the energy gap of the semiconductor alloy base to fix the Fermi level at a predetermined position. Can be achieved.

Also disclosed herein is a method of preventing charge fatigue in an electrophotographic medium of the type including a conductive substrate, a bottom charge injection barrier layer, a photoconductive layer and a surface protective layer. This method comprises forming an enhancement layer from a strongly doped semiconductor alloy material and operatively arranging the enhancement layer between the photoconductive layer and the surface protection layer to provide an interface at the interface between the enhancement layer and the surface protection layer. The step of configuring the enhancement layer to substantially reduce the number of charge carriers trapped in the deep intermediate gap trap upon approach. The method further comprises forming the bottom barrier layer from a boron-doped microcrystalline silicon / hydrogen / fluorine alloy, the degree of boron doping to degenerate the material, and the enhancement layer to an amorphous silicon alloy. And forming with a material selected from the group consisting essentially of amorphous germanium alloys and amorphous silicon-germanium alloys. In a preferred embodiment, the enhancement layer Elmi level is in the conduction or valence band range of 0.5 to 0.8 eV, preferably 0.65 to 0.75 eV.
Further included is the step of moving within the range. In this way, the material forming the enhancement layer is constructed so that the charge carrier emission from the trap takes place in about 1 second or less. The method may further include the step of forming the enhancement layer to have a thickness (approximately 2,500 to 10,000 angstroms, preferably approximately 5,000 angstroms. In a most preferred embodiment, the semiconductor alloy material forming the enhancement layer. Both the boron and phosphorus are introduced into the parent semiconductor matrix, and the Fermi level of the semiconductor alloy material is fixed by adding shallow states on both sides of the Fermi level in the energy gap.

DESCRIPTION OF SPECIFIC EMBODIMENTS BASED ON THE DRAWINGS Referring to the partial cross-sectional view of FIG. 1, there is shown a generally cylindrical electrophotographic photoreceptor 10 incorporating all of the innovative principles disclosed in this specification. There is. Photoreceptor 10
Includes a generally cylindrical substrate 12, which in this embodiment is made of aluminum, although non-deformed metals such as stainless steel can also be used as a preferred embodiment. The periphery of the aluminum substrate 12 is made a smooth and substantially defect-free surface by a well-known technique such as diamond processing and / or polishing. A doped layer 14 of microcrystalline semiconductor alloy is deposited directly above the deposition surface of substrate 12. This layer is configured to act as a bottom barrier layer for the photoreceptor 10. Similarly assigned US Pat. No. 4,58
According to the technique disclosed in US Pat. No. 2,773, the barrier layer 14 is formed of a highly doped high conductivity microcrystalline semiconductor alloy. A photoconductive layer 16 is provided directly above the bottom barrier layer 14. Photoconductive layer 16
Can be selected from a wide range of photoconductive materials. Some suitable materials include doped intrinsic amorphous silicon alloys, amorphous germanium alloys, amorphous silicon-germanium alloys, chalcogenides, organic photoconductive polymers, and the like. Located directly above the photoconductive layer 16 is the improved enhancement layer 18 of the present invention, which substantially reduces the problem of charge fatigue as described in the "Background of the Invention" section of the present invention. Is configured to. The photoreceptor 10 additionally includes a surface protective layer 19 disposed on the enhancement layer 18. The protective layer 19 serves to (1) protect the photoconductive layer surface from environmental conditions and (2) separate the charge stored on the surface of the photoreceptor 10 from the carriers created in the photoconductive layer 16.

In accordance with the principles of the first embodiment of the present invention, the enhanced enhancement layer 18 is formed of a heavily doped semiconductor alloy material. The purpose of strongly doping the enhancement layer 18 is to move the Fermi level near the conduction band of the semiconductor alloy forming the layer (when the corona charge is positive).
Obviously, if the surface charge is negative, it is desirable to heavily dope the enhancement layer 18 to bring the Fermi level of the semiconductor alloy for the enhancement layer formation closer to the valence band. A wide variety of semiconductor alloy materials can be used to form enhancement layer 18. Some suitable materials are silicon-hydrogen alloys, silicon-hydrogen-halogen alloys, germanium-hydrogen alloys, germanium-hydrogen-halogen alloys, silicon-germanium-hydrogen alloys, silicon-hydrogen-halogen alloys, and the like. Among the halogenated materials, a fluorine compound is particularly desirable.

Doping of semiconductor alloy materials can be done by and using techniques well known to those of ordinary skill in the art. The enhancement layer previously formed by the present inventor, as described in the above-mentioned U.S. Patent Application No. 580,081, was created with a low defect density, so that it moved from the photoconductive layer 16 through the enhancement layer to the surface protective layer. Charge carriers that neutralize the charge on the surface of 19 were not trapped in many deep intermediate gap traps. As a result, as described above, the number of charge carriers that take a long time to be released from the deep trap is reduced. Using the principle proposed in this patent application and the enhancement layer 18, the Fermi level of the enhancement layer 18 is moved and fixed if desired, against charge carriers, deep in the silicon alloy forming the layer. Since the intermediate gap state can be avoided, the charge carriers can be confined only in the shallow traps, and the residence time of the carriers in the traps is shortened. The lack of deeply confined carriers not only prevents the surface protection layer 20 from breaking, but also considerably lengthens the cycle time to recover the surface charge lost to the electrophotographic medium 10 and prepare for the next copy. Become.

Although a wide range of semiconductor materials can be selected to make photoconductive layer 16, amorphous silicon alloys, amorphous germanium alloys, and amorphous silicon-germanium alloys have been found to be particularly advantageous. Such alloys and their methods of manufacture are disclosed in the patents and patent applications incorporated by reference below.

The conductivity type of each material that creates the barrier layer 14 and photoconductive layer 16 is selected to provide a blocking contact between them,
Prevent the injection of unwanted charge carriers into the photoconductive layer 16. When the photoreceptor 10 is configured to be electrostatically charged with a positive charge, the bottom barrier layer 14 is formed of a strongly p-doped alloy and the photoconductive layer 16 is an intrinsic semiconductor layer, or n.
It is preferably formed of a doped semiconductor layer or a lightly p-doped semiconductor layer. The combination of these conductivity types results in substantial blocking of the flow of electrons from substrate 12 into photoconductive layer 16. Note that generally speaking, an intrinsic semiconductor layer or a lightly doped semiconductor layer is only suitable for forming the photoconductive layer 16 if it produces a lower rate of thermal charge carriers than if the material is more heavily doped. There is a need. The intrinsic semiconductor alloy layer is the most suitable because it has the smallest number of defects per unit volume and the best discharge characteristics.

When photoreceptor 10 is configured to be negatively charged, it is desirable to prevent holes from entering photoconductive layer 16. At this time, the conductivity types of the layers of the semiconductor alloy described above are opposite, but it is clear that the intrinsic material is still effective in this case as well.

The maximum electrostatic pressure (Vsat) that the photoreceptor 10 can withstand is the barrier layer.
Besides the efficiency of 14, it depends on the thickness of the photoconductive layer 16. When the efficiency of the barrier layer is constant, the thicker the photoconductive layer 16 is, the larger the withstand voltage of the photoreceptor 10 is. For this reason, the charge capacity or the charge acceptance amount is generally represented by a volt value per micron of the thickness of the photoconductive layer 16. In order to increase manufacturing economy and reduce stress, the photoconductive layer 16 should preferably have a total thickness of 25 microns or less. It is also desirable to maintain as high an electrostatic charge as possible on it. Therefore, increasing the efficiency of the barrier layer at a charge capacity of volts per micron means, in the meantime, an improvement in the performance of the photoreceptor. It has been found that photoreceptors constructed according to the principles of the present invention can withstand pressures above 50 volts per micron up to near the breakdown point of semiconductor alloys.

The strongly doped semiconductor alloy forming the enhancement layer of the present invention can be made by a wide range of deposition techniques well known to all those skilled in the art. Examples of these techniques are illustrative rather than limiting, and include chemical vapor deposition, light assisted chemical vapor deposition, sputtering, vapor deposition, electroplating, plasma spraying, free radical spraying, glow discharge deposition. Etc.

At the present time, it has been found that glow discharge deposition techniques are particularly useful for making the enhancement layers of the present invention. In the glow discharge deposition method, the substrate is placed in a chamber maintained below atmospheric pressure. A mixed process gas containing precursors (and dopants) of the semiconductor alloy to be deposited is introduced into the chamber and energized with electromagnetic energy. Electromagnetic energy activates the gas mixture of precursors to form ions and / or groups of materials and / or other active species that cause deposition of a layer of semiconductor material on the substrate. The electromagnetic energy used may be direct current energy such as radio frequency energy or microwave energy or alternating current energy.

Microwave energy has been found to be particularly advantageous in the manufacture of electrophotographic photoreceptors, as it allows rapid and economical continuous formation of layers of high quality semiconductor alloys.
Referring now to FIG. 2, there is shown a cross-sectional view of an apparatus configured to microwave bias deposit semiconductor layers onto a plurality of cylindrical drums or substrates 12. In this type of apparatus, the electrophotographic photoreceptor 10 of FIG. 1 can be advantageously manufactured.

Apparatus 20 includes a deposition chamber 22, which is configured to remove reaction products from a chamber suitably connected to a vacuum pump and to maintain proper pressure within the chamber to facilitate deposition. It has an exhaust port 24. The chamber 22 is also provided with a plurality of mixed reaction gas introductions 26, 28, 30 through which mixed reaction gases are introduced into the deposition environment.

A plurality of cylindrical drums or substrate members 12 are supported inside the chamber 22. The drums 12 are arranged in close proximity with their respective longitudinal axes substantially parallel and are closely spaced to form an interior chamber region 32 between the outer surfaces of adjacent drums. ing. To support the drum 12 in this manner, the chamber 12 includes a pair of upstanding walls.
One of these is shown as 34 in FIG. Each drum 12 is rotatably mounted on each main shaft 38 by a pair of disk-shaped spacers 42, and the outer dimensions of the spacers 42 correspond to the inner dimensions of the drum 12 to frictionally engage them. The spacers 42 are driven by a motor (not shown) and chain conduction to facilitate the uniform deposition of material on the entire outer surface of the cylindrical drum 12 by rotating it during the coating process.

As mentioned above, the drum 12 is closely spaced on its outer surface to form an inner chamber 32. As can be seen from FIG. 2, the reaction gas, which is the formation source of the deposition plasma, has a plurality of narrow passages formed between the pair of adjacent drums 12.
It is introduced into the inner chamber 32 through at least one of the 52. At this time, it is desirable that the narrow passages 52 are introduced into the inner chamber 32 through every other passage.

As can be seen from FIG. 2, a gas shroud 54 is provided for each pair of adjacent drums, and a conduit is provided for each shroud.
It is connected by 56 to one of the inlets 26, 28, 30. Each shroud 54 forms a reaction gas storage portion 58 adjacent to a narrow passage through which the reaction gas to be introduced passes. Shroud 54
The shroud extension also includes side extensions 60 that extend from both sides of the reservoir 58 along the circumference of the drum 12.
A narrow channel 62 is formed between 60 and the outer surface of drum 12. By making the shroud 54 as described above, most of the reaction gas flows into the inner chamber 32,
It is possible to maintain a uniform gas flow across the 12 lateral spreads.

As can be seen, the narrow passages 66 that are not used to introduce reaction gas into the inner chamber 32 are used to remove reaction products from the inner chamber 32. When the pump connected to the exhaust port 24 is energized, it is exhausted from the inside of the chamber 22 and the internal chamber 32 through the narrow passage 66. In this way, the reaction product can be withdrawn from the chamber 22 while maintaining the internal chamber 32 at a pressure suitable for deposition.

In order to facilitate the generation of precursor free radicals and / or ions and / or other active species from the mixed process gas, the device further comprises a microwave energy source such as a magnetron with a waveguide assembly or antenna. And is arranged to provide microwave energy to the interior chamber 32. As shown in FIG. 2, the device 20 includes a window 96 formed of a microwave transparent material such as glass or quartz. The window 96 surrounds the inner chamber 32 and allows the placement of a magnetron or other source of microwave energy outside the chamber 22 to isolate it from the mixed process gas environment.

It is desirable to maintain the drum 12 at an elevated temperature during the deposition process. Therefore, the device 20 may be provided with a plurality of heating elements (not shown) to heat the drum 12. When depositing amorphous semiconductor alloys, the drum is generally 20 to 400 ° C.
To about 225 ° C.

Example In this example, an electrophotographic photoreceptor was prepared in a microwave energized glow discharge system generally similar to that described with reference to FIG. First, place a clean aluminum substrate in the deposition equipment, then depressurize the chamber and place it in hydrogen.
A mixed gas containing 0.15 SCCM (standard cubic centimeters / minute) containing 0.8% BF ₃ , 75 SCCM containing 1000 ppm SiH ₄ in hydrogen, and 45 SCCM hydrogen was introduced. The total pressure inside the chamber is maintained at about 100 microns by adjusting the intake / exhaust rate at a constant level, while the substrate temperature is maintained at about 300 ° C.
Maintained at. A bias of +80 volts was set by placing a charging wire in the plasma region. 2.45GHz
Of microwave energy was introduced into the deposition area. As a result of these conditions, a bottom barrier layer of microcrystalline silicon-hydrogen-fluorine alloy material doped with boron was formed. The deposition rate was approximately 20 Å / sec and deposition was continued until the total thickness of the boron-doped microcrystalline barrier layer reached approximately 7500 Å.

At this point, the microwave energy was stopped, and the mixed reaction gas flowing in the room was prepared by mixing 0.18% BF ₃ in hydrogen 0.5
The SCCM and SiH ₄ were changed to a mixture consisting of 30 SCCM and SiF _{4 4} SCCM and 40 SCCM hydrogen. Maintain pressure at 50 microns, 2.
45 GHz microwave energy was introduced into the device. This resulted in the deposition of a layer of lightly p-doped amorphous silicon / hydrogen / fluorine alloy material. Deposition of this alloy material (which forms the photoconductive layer of the electrophotographic medium) was continued at a rate of approximately 100 Å / sec until approximately 20 microns of amorphous silicon alloy was deposited.

To carry out the deposition of an amorphous silicon alloy to form the improved enhancement layer of the present invention, a sufficient amount of phosphorus obtained from the phosphine gas is added to bring the Fermi level of the deposited alloy to approximately 0.75-0.65 from its conduction band. It is necessary to move to eV. In order to achieve both the movement of the Fermi level in this way and the fixing of the Fermi level at this position so that the Fermi level does not bisect during illumination, the Fermi level of 0.75 to 0.65 eV After moving to the range, approximately equal amounts of phosphine gas and boron trifluoride gas are introduced into the precursor mixture gas. The other deposition parameters remain the same as in the previous section.

Amorphous silicon / carbon / on top of the improved enhancement layer
Deposit a surface protective layer of hydrogen / fluorine alloy. 2SCCM SiH
_A mixed gas containing ₄ and 30 SCCM of CH ₄ and 2 SCCM of SiF ₄ is introduced into the deposition apparatus to deposit the surface protective layer. Next, when the microwave energy source is activated, the amorphous silicon / hydrogen / fluorine / carbon layer is almost 40 angstroms /
It was deposited at a rate of seconds. Deposition is continued until a protective layer of approximately 5000 angstroms is deposited, and when that thickness is reached, microwave energy is stopped and the substrate is placed at 100 ° C
The system pressure was raised to atmospheric pressure. The electrophotographic photoreceptor thus prepared was taken out and tested.
Obviously, the above methods can be modified, and it is also possible to produce a photoreceptor configured to be negatively charged by simply changing to approximately equimolar amounts of opposite dopants. That is, the bottom barrier layer is a phosphorus-doped layer, the photoconductive layer is an intrinsic or lightly phosphorus-doped layer, and the Fermi level of the enhancement layer is positioned and fixed within the range of 0.65 to 0.75 eV of the valence band.

It should be understood that many changes and modifications can be made to the configurations described above within the scope of the present invention. Although the examples given above are intended for electrophotographic photoreceptors formed of amorphous silicon alloys, the present invention is not of course limited thereto, and includes chalcogenized photoconductive materials and organic photoconductors. It can be utilized in connection with the manufacture of various photoreceptors containing a variety of photoconductive materials such as conductive materials. The barrier layers described herein can be made from a wide range of microcrystalline semiconductor alloys in the spirit of the invention.

The drawings, the description, the description and the examples described above are all for explaining the present invention and are not intended to limit the implementation of the present invention.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an electrophotographic photoreceptor including the improved enhancement layer of the present invention, and FIG. 2 is a microwave configured to produce the electrophotographic photoreceptor as shown in FIG. It is a schematic sectional drawing of a glow discharge deposition apparatus. 10 ... Photoreceptor, 12 ... Substrate, 14 ... Bottom barrier layer, 16 ...
… Photoconductive layer, 18… Enhancement layer, 19… Surface protection layer, 20… Photoreceptor manufacturing device, 22… Deposition chamber.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Stephen Jay Hadgens United States, Michigan 48075, Southfield, Aligzan Doria Tone 2 (56) References JP 60-83957 (JP, A) JP-A-60-112048 (JP, A) JP-A-60-59367 (JP, A) JP-A-57-115552 (JP, A)

Claims (6)

[Claims] 1. A medium for an electrophotographic apparatus for imparting a first conductivity type charge to a medium having a bottom barrier layer, a photoconductive layer and a surface protective layer on a conductive substrate, wherein the photoconductive layer and the photoconductive layer are provided. A semiconductor layer made of an amorphous material containing silicon is provided between the surface protection layer and a dopant capable of moving the Fermi level of the semiconductor layer, and the semiconductor layer has a conductivity type opposite to the first conductivity type. A medium for an electrophotographic apparatus, characterized in that the medium is doped. 2. The electrophotographic device is a device for imparting a positive charge, and the Fermi level of the semiconductor layer is within the range of 0.5 to 0.8 eV from the conduction band due to phosphorus as the dopant. The medium for the electrophotographic apparatus according to Item 1. 3. The electrophotographic device is a device for imparting a positive charge, and the Fermi level of the semiconductor layer is within the range of 0.65 to 0.75 eV from the conduction band due to phosphorus as the dopant. The medium for the electrophotographic apparatus according to Item 1. 4. The electrophotographic device is a device for imparting a negative charge, and the Fermi level of the semiconductor layer is within a range of 0.5 to 0.8 eV from a valence band due to boron as the dopant. The medium for the electrophotographic apparatus according to Item 1. 5. The electrophotographic device is a device for imparting a negative charge, and the Fermi level of the semiconductor layer is 0.65 to 0.75 eV from the valence band due to boron as the dopant.
A medium for an electrophotographic apparatus according to claim 1, which is within the scope of. 6. An electrophotographic apparatus for imparting a first conductivity type charge to a medium having a bottom barrier layer, a photoconductive layer and a surface protective layer on a conductive substrate, wherein the medium is the photoconductive layer. A semiconductor layer made of an amorphous material containing silicon is provided between the surface protection layer and
An electrophotographic apparatus, wherein the semiconductor layer is a medium in which the semiconductor layer is doped with a conductivity type opposite to the first conductivity type with a dopant capable of moving the Fermi level of the semiconductor layer.